Adjusting and locking arrangement for variable impedance devices



Flled Feb 27 1964 VARIABLE IMPEDANCE DEVICES F. LYMAN, JR ADJUSTING AND LOCKING ARRANGEMENT FOR INVENTOR. 9mm; JF: BY

LIZ/U United States Patent 3,302 150 ADJUSTING AND LOCKING ARRANGEMENT FOR VARIABLE IMPEDANCE DEVICES Frank Lyman, In, Cambridge, Mass, assignor to Cambridge Thermionic Corporation, Cambridge, Mass, a

corporation of Massachusetts Filed Feb. 27, 1964, Ser. No. 347,809 14 Claims. (Cl. 336136) The field of this invention relates to variable impedance devices of the type which have an impedance component such as a plug relatively movable within a second component such as a sleeve, for example coil forms and capacitors.

Previously known impedance devices of the above type have been adjusted by moving the impedance plug within the sleeve to the desired position. However, such prior devices have not satisfactorily maintained this adjustment when subjected to substantial vibration, temperature variation or both.

Objects of the present invention are accordingly to provide a variable impedance device especially adapted to maintain a predetermined relative position between two relatively movable components when exposed to vibration and temperature change; to provide such devices which are easy to manufacture, assemble, adjust and lock in a predetermined tuning position; and to accomplish these functions with simple, inexpensive and yet fully reliable expedients.

The substance of the invention for obtaining the above objects may be summarized as follows:

Impedance devices according to this invention have two relatively movable electrically effective components such as an impedance sleeve and an impedance plug axially movable within the sleeve, and at least one jam plug with threads which engage threads on the sleeve or the impedance plug, or both. The jam plug threads are of different pitch from the engaging threads of the sleeve or impedance plug. By being thus cross-threaded, the jam plug will tightly engage its mating element to firmly lock the impedance plug in predetermined position relative to the sleeve.

Preferably, the jam plug is of a material having a different coefficient of thermal expansion than the element with which it is cross-threaded. For use at temperatures expected to be below assembly temperature, the finer thread, that is the thread having the smaller pitch, is provided in the cross-threaded element having the higher coetficient. Conversely, when use temperatures above assembly temperatures are expected, the coarser thread is provided in the higher coeflicient material. By this means,

the device is temperature compensating; at lower temperatures the finer threads shrink the greater amount, while at higher temperature the coarser threads expand the greater amount, in either case more firmly to lock the elements in position.

It is further preferred that the jam plug comprise a material more resilient than the impedance plug or sleeve. Also, if desired, a resilient bumper which maintains its resilience at the contemplated temperature of use may be interposed between adjacent faces of the impedance HQ. 4 is an axial section of a third embodiment of the lnvention.

Referring to FIG. 1, the impedance device 10 comprises a sleeve 11 having a substantially uniform internal thread 12, an impedance plug 13' having mating external threads 14, a jam plug 15 having external threads 16. A resilient bumper 17 can be interposed between adjacent faces of the plugs 13 and 15, although it can be dispensed with depending on the intended use and the construction materials selected for such use. Threads 16 on jam plug 15 are engageable with sleeve thread 12 but differ in pitch therefrom so as to be cross-threaded and frictionally locked therewith in position to apply locking thrust to the bumper 17 and the end face of plug 13. Plugs 13 and 15 are provided with recesses or slots 18 to facilitate turning by means of a screwdriver or the like for adjustment.

In use, impedance plug 13 is inserted within sleeve 11 and turnedto the desired turning position. Thereafter jam plug 15 is inserted in sleeve 11 and turned until it firmly engages bumper 17 and the end face of plug 13 to lock them in position. In the coil forms illustrated, conductor windings 20 are carried on the exterior surface of sleeve 11, and electrical input and output terminals (not shown) are provided in known manner.

Preferably jam plug 15 or at least a portion thereof which is effective in the herein described sense is made of a material different from and having a different, preferably higher coefficient of thermal expansion than sleeve 11. The material having the higher coefficient of thermal expansion should have the finer thread where use is contemplated at reduced temperatures, and conversely, the material having the higher coefficient of thermal expansion should have the coarser thread where use at elevated temperatures is to be expected. The terms reduced and elevated temperatures as used herein are in comparison with the temperature during original adjustment which will normally be ambient temperature approximating 70 F.

At present, coil forms of the type shown in FIG. 1 typically comprise sleeves 11 of ceramic material which is relatively brittle and of low coefficient of thermal expansion. Impedance plugs 13 are commonly of powdered iron which has a higher coefficient. With such devices the most serious problem of locking is encountered when the device is subjected to extremely low temperatures, for example, in space. At such temperatures the iron plug 13 will shrink and become progressively looser within the bore of sleeve 11. With devices of this type, jam plug 15 is preferably of a synthetic plastic material having a relatively high coefficient of thermal expansion and which is more resilient than the ceramic sleeve 11. As plug 15 shrinks in diameter at reduced temperature, its finer threads simultaneously shrink and engage the coarser ceramic threads more firmly and thereby compensate and maintain the impedance plug 13 in locked position.

In one typical example, the ceramic sleeve 11 was provided with shallow No. 10-32 threads 12, the powdered iron impedance plug 13 was provided with complementary shallow No. 10-32 threads 14, in accordance with Powdered Metal Association standards, and the plastic jam plug 15, for example Kel-F, was provided with No. 10-30 threads 16. This unit withstood vibration at minus 55 C., whereas a corresponding test with No. 10-32 threads on a jam plug resulted in failure.

In the embodiment shown in FIG. 2, the impedance plug 21 is unthreaded but well fitted and two jam plugs 1515 are provided, one at either end of plug 21 to apply opposed anchoring thrust thereon. Adjustment of the relative position of plug 21 within sleeve 11 is then accomplished by the adjustment, preferably simultaneously, of the two jam plugs 15-15. Each of jam plugs 15-15 are provided with threads of different pitch from the engaging threads 12 of sleeve 11 and are preferably of a different material having a different coefficient of thermal expansion in the same manner as described in FIG. 1.

In the embodiment shown in FIG. 4, the jam plug is employed to lock a movable impedance plug in a variable capacitor. The Capacitor comprises an insulating sleeve 25 having a mounting extension 26 with exteriorly threaded portion 27 extending therefrom, extension 26 being crimped over the enlarged portion 28 of sleeve 25. A portion of the exterior surface of sleeve 25 is provided with a conductive layer 30 having an electrical lead 31. Axially movable with sleeve 25 is a capacitor plate element or plug 32 which may be of the type shown, for example, in United States Patent No. 2,910,635. Plug 32 has a projecting lead screw 33 which is threaded through extension 26 for relative adjustment of the position of plug 32 within sleeve 25. I am plug 34 has interior threads engageable with the exterior threads of lead screw 33. The interior threads of the jam plug 34 are of a different pitch from the lead screw 33 to provide a cross-thread therewith for locking. Plug 34 is provided with slots 35 and 36 for receiving a turning device such as a spanner wrench for turning plug 34 within extension 27. The end face 34.1 of plug 34 opposite slots 35 and 36 abuts the face 26.1 of extension 26 and thereby locks impedance plug 32 in predetermined position relative to sleeve 25. However, it is preferred that plug 34 also carry external threads on its outer circumference, engageable with, but also of different pitch from, internal threads 38 within the extension 27 for more positive locking of the plug 32 within sleeve 25.

The device shown in FIG. 4 may be mounted in the conventional manner, for example, by inserting extension 27 through an opening in a panel wall and securing the device thereto by means of a nut engaging the exterior threads on extension 27.

In each of the foregoing embodiments, the jam plug is preferably of a material having a different coefficient of thermal expansion from the element with which its threads engage for locking. The material having the higher coefficient of thermal expansion should have the finer threads when the device is to be used at reduced temperatures, and conversely, should have coarser thread when the device is designed for use at elevated temperatures. Preferably, the jam plug in each case comprises a resilient material having the higher coefficient of thermal expansion and is preferably a non-magnetic insulator so as not to affect the overall impedance.

Bumpers 17, shown in FIGS. 1 and 2, should comprise a resilient material which maintains its resilience at all contemplated temperatures of use. For example, a silicone rubber can be employed for low temperature use. The bumper can be merely placed in position between the two abutting elements, or may be bonded to one or the other of the abutting faces. The use of such bumpers is not essential, but is often preferred since it aids in compensating for change of size with varying temperature, of most materials used for present purposes.

It should be understood that the foregoing description is for the purpose of illustration only and that the invention includes all modifications falling within the scope of the appended claims.

I claim:

1. A variable inductance device comprising:

a ceramic impedance sleeve having substantially uniform internal threads,

an impedance plug of magnetic metal having substantially uniform exterior threads engaging said internal threads for axially adjusting the position of the impedance plug with the sleeve, and

at least one jam plug of non-magnetic material more resilient than the sleeve, said jam plug having exterior threads engageable with but of greater pitch than the interior threads of said sleeve, said material having a higher coefficient of thermal expansion than said sleeve,

wherebly said jam plug is frictionally held in predetermined position within the sleeve to exert locking thrust on said impedance plug.

2. A variable inductance device comprising:

an impedance sleeve having substantially uniform internal threads,

an impendance plug axially movable within said sleeve,

and

two jam plugs within the sleeve, one on either side of said impedance plug, said jam plugs having external threads of a pitch different from but engageable with the interior threads of said sleeve, said jam plugs exerting opposed thrusts on said impedance plug to lock it in predetermined position within said sleeve.

3. A device according to claim 2, wherein said impedance plug is unthreaded.

4. A device according to claim 2, wherein a resilient bumper is disposed between adjacent faces of the impedance plug and at least one jam plug.

5. A device according to claim 2, adapted for use at reduced temperatures, wherein said internal and external engaging threads are of different materials having different coefficients of thermal expansion, the material having the higher coefficient having the finer threads.

6. A device according to claim 2, adapted for use at elevated temperatures, wherein said internal and external threads are of different materials having different coefficients of thermal expansion, the material having the higher coefficient of expansion having the coarser threads.

7. A variable inductance device comprising:

a ceramic impedance sleeve having substantially uniform internal threads,

an unthreaded impedance plug of magnetic material axially movable within said sleeve, and

at least two jam plugs of a non-magnetic material having a higher coefficient of thermal expansion than the material comprising said sleeve, said jam plugs having external threads finer than but engageable with said internal sleeve threads, said jam plugs being disposed one on either side of said impedance plug to exert opposed, locking thrusts thereon to maintain the same in predetermined position within said sleeve.

8. A variable condenser especially adapted for use at reduced temperatures comprising:

an impedance sleeve having a conductor on a portion of its surface and having an internally threaded portion,

an impedance plug axially movable within said sleeve and having an externally threaded portion, and a jam plug axially movable within said internally threaded sleeve portion and of a material more resilient and having a higher coefficient of thermal expansion than the materials comprising said sleeve portion and impedance plug, said jam plug having internal and external threads of finer pitch but engageable with said external impedance plug and internal sleeve threads, respectively, and said jam plug frictionally locking said impedance plug in predetermined position within said sleeve. 9. A variable impedance device comprising: a threaded impedance sleeve, a threaded impedance plug axially movable within said sleeve, I

at least one jam plug having threads engaged by threads on said impedance sleeve, said jam plug threads being of a pitch different from said engaged threads, and

the engaging threads on said jam plug and on said impedance sleeve being of materials respectively having different coefficients of thermal expansion, the material having the higher coefficient being provided with the finer threads,

whereby said jam plug is frictional'ly held in predetermined position relative to said sleeve and locks the impedance plug in a predetermined position within the sleeve.

10. A variable impedance device comprising:

a threaded impedance sleeve,

a threaded impedance plug axially movable within said sleeve,

at least one jam plug having threads engaged by threads on said impedance sleeve, said jam plug threads being of a pitch different from said engaged threads, and

the engaging threads on said jam plug and on said impedance sleeve being of materials respectively having different coefiicients of thermal expansion, the material having the higher coefficient having the coarser threads,

whereby said jarn plug is 'frictionally held in predetermined position relative to said sleeve and locks the impedance plug in a predetermined position within the sleeve.

11. A coil for-m variable impedance device comprisan impedance sleeve having substantially uniform interior threads,

an impedance plug having substantially uniform exterior threads engaging said interior threads for axially adjusting the position of the impedance plug within the sleeve,

at least one jam plug having exterior threads of a pitch difierent from but engageable with said interior threads of the sleeve to apply locking thrust to said impedance plug in predetermined position within said sleeve, and

the threads of said sleeve and the threads of said jam plug being of materials having different coefficients of thermal expansion, the material of the jam plug threads having the higher coelificient and having a pitch greater than but engageable with, the sleeve threads.

12. A coil form variable impedance device comprisan impedance sleeve having substantially uniform interior threads,

an impedance plug having substantially uniform exterior threads engaging said interior threads for axially adjusting the position of the impedance plug within the sleeve,

at least one jam plug having exterior threads of a pitch different from but engageable with said interior threads of the sleeve to apply locking thrust to said impedance plug in predetermined position within said sleeve, and

the threads of said sleeve and the threads of said jam plug being of materials having different coeflicients of thermal expansion, the material of the jam plug threads having the higher coefiicient and having a pitch less than, but engageable with, the sleeve threads.

13. A variable capacitance device comprising:

an impedance sleeve,

an impedance plug axially movable within said sleeve and having a threaded portion, and

a jam plug with threads of a pitch different from, but engageable' with, said impedance plug threads and including a material having a higher coefficient of thermal expansion and having a higher pitch than the threads of the impedance plug whereby the threads engage more tightly at reduced temperature, said jam plug having means engaging said sleeve to lock the sleeve and impedance plug in predetermined relative position.

14. A variable capacitance device comprising:

an impedance sleeve,

an impedance plug axailly movable Within said sleeve and having a threaded portion, and

a jam plug with threads of a pitch different from, but engageable with, said impedance plug threads and including a material having a higher coelficient of thermal expansion and having a lesser pitch than the threads of the impedance plug whereby the threads engage more tightly at elevated temperature, said jam plug having means engaging said sleeve to lock the sleeve and impedance plug in predetermined relative position.

References Cited by the Examiner UNITED STATES PATENTS 2,207,783 7/1940 Carlson et al. 317-247 3,070,765 12/1962 Johansson 336-134 X 3,105,948 10/1963 McFarlane 336l36 FOREIGN PATENTS 876,636 9/1961 Great Britain. 886,500 5/1943 France.

LEWIS H. MYERS, Primary Examiner.

JOHN F. BURNS, Examiner.

C. TORRES, Assistant Examiner. 

1. A VARIABLE INDUCTANCE DEVICE COMPRISING: A CERAMIC IMPEDANCE SLEEVE HAVING SUBSTANTIALLY UNIFORM INTERNAL THREADS, AN IMPEDANCE PLUG OF MAGNETIC METAL HAVING SUBSTANTIALLY UNIFORM EXTERIOR THREADS ENGAGING SAID INTERNAL THREADS FOR AXIALLY ADJUSTING THE POSITION OF THE IMPEDANCE PLUG WITH THE SLEEVE, AND AT LEAST ONE JAM PLUG OF NON-MAGNETIC MATERIAL MORE RESILIENT THAN THE SLEEVE, SAID JAM PLUG HAVING EXTERIOR THREADS ENGAGEABLE WITH BUT OF GREATER PITCH THAN THE INTERIOR THREADS OF SAID SLEEVE, SAID MATERIAL HAVING A HIGHER COEFFICIENT OF THERMAL EXPANSION THAN SAID SLEEVE, WHEREBY SAID JAM PLUG IS FRICTIONALLY HELD IN PREDETERMINED POSITION WITHIN THE SLEEVE TO EXERT LOCKING THRUST ON SAID IMPEDANCE PLUG. 